Machines such as wheel loaders, dozers, off-highway trucks, and other heavy equipment are used to perform many tasks. To effectively perform these tasks, the machines require an engine that provides significant torque through a transmission to one or more ground engaging devices. In order to control the speed and torque output of the ground engaging devices, the operator of these machines is typically provided with three different foot pedals. One of the three pedals is actuated to affect engine fueling. Another of the three pedals is actuated to affect vehicle braking. The third of the three pedals is actuated to disengage the engine from the transmission and, if depressed enough, also affects vehicle braking.
Although this configuration may be suitable when a mechanical, step-change transmission is utilized to transmit power from the engine to the ground engaging devices, it may be insufficient and/or cumbersome when a continuously variable transmission (CVT) is utilized. A CVT is an automatic type of transmission that provides an infinite number of output ratios within its ratio range. For example, a hydraulic CVT can include a pump and a fluid motor that receives pressurized fluid from the pump. Depending on a discharge flow rate and pressure of the pump, the motor speed and output torque at the ground engaging device may be varied. When using a CVT, a primary goal is to keep the engine as efficiently stable as possible. In this situation, the strategy described above of constantly changing engine fueling and/or constantly disconnecting the engine from the transmission may work against the efficiency goal. Therefore, an alternative strategy is required to efficiently control operation of a machine utilizing a CVT.
An alternative method of powertrain control is described in U.S. Pat. No. 7,854,681 of Sopko et al. that issued on Dec. 21, 2010 (the '681 patent). The '681 patent describes a machine having a CVT, left and right operator pedals, a gear selector, and a controller in communication with the CVT, the pedals, and the gear selector. The left foot pedal generates a first signal indicative of a desired amount of power that should be transmitted to propel the machine. The right foot pedal generates a second signal indicative of a desired engine speed. The gear selector generates a third signal associated with a travel speed limit of the machine. The controller generates a torque output command for the CVT that is a function of the first and second signals. The torque output command is then modified based on the third signal. The machine also includes a throttle lock feature that allows the operator of the machine to lock an engine speed at a desired level, while allowing independent control of the CVT. The throttle lock feature may allow for operation of the machine without manual manipulation of the right foot pedal.
Although the system of the '681 patent may provide for efficient regulation of a CVT, it may still be less than optimal. In particular, the operator is still required to modulate the left foot pedal during operation, which can be cumbersome and tiring for the operator. In addition, there may be times when the operator-selected engine speed (i.e., the engine speed selected via the throttle lock feature) is inefficient for current operations and the system of the '681 patent does not provide a way to override this feature.
The powertrain control system of the present disclosure solves one or more of the problems set forth above and/or other problems of the prior art.